Hydro‐climatic variability and trends in Washington State for the last 50 years

Historical records of monthly streamflow and precipitation coupled with mean, minimum, and maximum air temperatures for Washington State were used to study the variation and the trend characteristics that occurred over the last 50 years (1952–2002). Results indicate that the 1967 statewide water resource assessment needs to be updated because all of the stations used in that study exhibited a decreasing trend in annual streamflow ranging from ?0·9% to ?49·3%, with an arithmetic mean of ?11·7% and a median value of ?9·8%. Furthermore, a slightly decreasing trend in annual streamflow, although not statistically significant, was detected. The decreasing streamflow magnitude was about ?1·178 mm year^?2, or 4·88 m³ s^?1 year^?1, which caused a decrease in annual streamflow in the state of about 58·9 mm, or 244 m³ s^?1. This magnitude was about 9·6% of the average annual streamflow for the entire state from 1952 to 2002. Contrastingly, the overall annual precipitation in the entire state increased 1·375 mm year^?2. Overall the annual means of daily mean, maximum, and minimum temperature increased by 0·122, 0·048, and 0·185 °C/10 years, respectively, during the study period. Thus the corresponding annual means of daily mean, maximum, and minimum temperatures increased by 0·61, 0·24, and 0·93 °C, respectively. All of these trends and magnitudes were found to vary considerably from station to station and month to month. The possible reasons resulting in these detected trends include, but are not limited to, human activities, climate variability and changes, and land use and land cover changes. Copyright © 2009 John Wiley & Sons, Ltd.     

Separating the effects of changes in land management and climatic conditions on long‐term streamflow trends analyzed for a small catchment in the Loess Plateau region,NW China

As an integrated result of many driving factors, significant declines in streamflow were observed in many rivers of the Loess Plateau (NW China). This can aggravate the inherent severe water shortages and threatens the regional development. Therefore, it is urgent to develop adaptive measures to regulate the water yield to ensure water security. A key step for successful implementation of such measures is to separate the response of water yield to the main driving factors of land management and climate change. In this study, the variation of annual streamflow, precipitation, potential evapotranspiration, and climatic water balance in a small catchment in the Loess Plateau (near Pingliang, Gansu province) was examined for over five decades, although the relative contribution of changes in land management and climate on the streamflow reduction were estimated. A statistically significant decreasing trend of ‐1.14 mm y^‐1 in annual streamflow was detected. Furthermore, an abrupt streamflow reduction because of construction of terraces and check‐dams was identified around 1980. Remarkably, 74% of the total reduction in mean annual streamflow can be attributed to the soil conservation measures. Based on a literature review across the Loess Plateau, we found that the impact of changes in land management and climate on annual streamflow diminished with increasing catchment size. This means that there is a dependency on catchment size for the hydrological response to environmental change. This indicates that at least at the local scale well‐considered land management may help ensure the water security at the Loess Plateau. Copyright © 2012 John Wiley & Sons, Ltd.     

Multi‐temporal scale changes of streamflow and sediment load in a loess hilly watershed of China

Global climate change and diverse human activities have resulted in distinct temporal–spatial variability of watershed hydrological regimes, especially in water‐limited areas. This study presented a comprehensive investigation of streamflow and sediment load changes on multi‐temporal scales (annual, flood season, monthly and daily scales) during 1952–2011 in the Yanhe watershed, Loess Plateau. The results indicated that the decreasing trend of precipitation and increasing trend of potential evapotranspiration and aridity index were not significant. Significant decreasing trends (p < 0.01) were detected for both the annual and flood season streamflow, sediment load, sediment concentration and sediment coefficient. The runoff coefficient exhibited a significantly negative trend (p < 0.01) on the flood season scale, whereas the decreasing trend on the annual scale was not significant. The streamflow and sediment load during July–August contributed 46.7% and 86.2% to the annual total, respectively. The maximum daily streamflow and sediment load had the median occurrence date of July 31, and they accounted for 9.7% and 29.2% of the annual total, respectively. All of these monthly and daily hydrological characteristics exhibited remarkable decreasing trends (p < 0.01). However, the contribution of the maximum daily streamflow to the annual total progressively decreased (?0.07% year^?1), while that of maximum daily sediment load increased over the last 60 years (0.08% year^?1). The transfer of sloping cropland for afforestation and construction of check‐dams represented the dominant causes of streamflow and sediment load reductions, which also made the sediment grain finer. Copyright © 2015 John Wiley & Sons, Ltd.     

Runoff modifications due to the conversion of natural grasslands to forests in a large basin in Uruguay

Uruguay has encouraged the development of the forestry sector since 1989. As a member of the Montreal Process, the country has followed a set of criteria and indicators for the Sustainable Forest Management. The aim of this paper is to describe the studies carried out in a large basin of 2097 km², located in an area of humid subtropical climate and 1300 mm of long‐term mean annual rainfall, where the conversion of natural grasslands to forests increased up to 540 km² during the last 15 years. Using data from daily rainfall and streamflow, the study analyses the effects of afforestation on the runoff and water loss. The analysis comprises hydrographs resulting from comparable rainfall events and annual and seasonal streamflow and water loss behaviour, both before afforestation (1975–1993) and during the afforestation period (1994–2008). A statistically significant reduction of runoff volumes (33–43%) and peak flows (59–65%) were identified on storm hydrographs. The annual and seasonal streamflow also showed diminishing tendencies due to the forestry development, whereas the water loss increases. The annual streamflow decreased between 8·2 and 36·5% depending on the annual rainfall totals. The streamflow reduction was higher during spring and summer (25·2–38·4%) and smaller during autumn and winter (15–20·3%). The water loss is expected to increase by 98 mm for the long‐term mean annual rainfall. The resulting information is a valuable input for the Integrated Water Resources Management of the Negro river basin located downstream, where hydroelectric power, rice irrigation and forestry development are supported. Copyright © 2008 John Wiley & Sons, Ltd.     

Understanding changes in annual runoff following land use changes: a systematic data‐based approach

A simple modelling framework for assessing the response of ungauged catchments to land use change in South‐Western Australia is presented. The framework uses knowledge of transpiration losses from native vegetation and pasture and then partitions the ‘excess’ water (resulting from reduced transpiration after land use change) between runoff and deep storage. The simple partitioning is achieved by using soft information (satellite imagery, previous mapping and field assessment) to delimit the spread of the permanently saturated area close to the stream. Runoff is then assumed to increase in proportion to the saturated area, with the residual difference going to deep storage. The model parameters to describe the annual water yield are obtained a priori and no calibration to streamflow is required. We tested the model using gauged records over 25 years from paired catchment experiments in South‐Western Australia. Very good estimates of runoff were obtained from high rainfall (>1100 mm yr⁻¹) catchments (R² > 0·9) and for low rainfall (<900 mm yr⁻¹) catchments after clearing (R² = 0·96) but results were poorer (R² = 0·55) for an uncleared low rainfall catchment, although overall balances were reasonable. In the drier uncleared catchments, the within‐year distributions of rainfall may exert a substantial influence on runoff response that is not completely captured by the presented model. Copyright © 2005 John Wiley & Sons, Ltd.     

Changes in streamflow regime following vegetation changes from paired catchments

Vegetation changes can significantly affect catchment water balance. It is important to evaluate the effects of vegetation cover change on streamflow as changes in streamflow relate to water security. This study focuses on the use of statistical methods to determine responses in streamflow at seven paired catchments in Australia, New Zealand, and South Africa to vegetation change. The non‐parametric Mann–Kendall test and Pettitt's test were used to identify trends and change points in the annual streamflow records. Statistically significant trends in annual streamflow were detected for most of the treated catchments. It took between 3 and 10 years for a change in vegetation cover to result in significant change in annual streamflow. Presence of the change points in streamflow was associated with changes in the mean, variance, and distribution of annual streamflow. The streamflow in the deforestation catchments increased after the change points, whereas reduction in streamflow was observed in the afforestation catchments. The streamflow response is mainly affected by the climate and underlying vegetation change. Daily flow duration curves (FDCs) for the whole period and pre‐change and post‐change point periods also were analysed to investigate the changes in flow regime. Three types of vegetation change effects on the flow regime have been identified. The relative reductions in most percentile flows are constant in the afforestation catchments. The comparison of trend, change point, and FDC in the annual streamflow from the paired experiments reflects the important role of the vegetation change. Copyright © 2011 John Wiley & Sons, Ltd.     

Simulated water budget of a small forested watershed in the continental/maritime hydroclimatic region of the United States

Annual streamflows have decreased across mountain watersheds in the Pacific Northwest of the United States over the last ~70 years; however, in some watersheds, observed annual flows have increased. Physically based models are useful tools to reveal the combined effects of climate and vegetation on long‐term water balances by explicitly simulating the internal watershed hydrological fluxes that affect discharge. We used the physically based Simultaneous Heat and Water (SHAW) model to simulate the inter‐annual hydrological dynamics of a 4 km² watershed in northern Idaho. The model simulates seasonal and annual water balance components including evaporation, transpiration, storage changes, deep drainage, and trends in streamflow. Independent measurements were used to parameterize the model, including forest transpiration, stomatal feedback to vapour pressure, forest properties (height, leaf area index, and biomass), soil properties, soil moisture, snow depth, and snow water equivalent. No calibrations were applied to fit the simulated streamflow to observations. The model reasonably simulated the annual runoff variations during the evaluation period from water year 2004 to 2009, which verified the ability of SHAW to simulate the water budget in this small watershed. The simulations indicated that inter‐annual variations in streamflow were driven by variations in precipitation and soil water storage. One key parameterization issue was leaf area index, which strongly influenced interception across the catchment. This approach appears promising to help elucidate the mechanisms responsible for hydrological trends and variations resulting from climate and vegetation changes on small watersheds in the region. Copyright © 2015 John Wiley & Sons, Ltd.     

Streamflow regimes of the Yanhe River under climate and land use change,Loess Plateau,China

Soil and water conservation measures including terracing, afforestation, construction of sediment‐trapping dams, and the ‘Grain for Green Program’ have been extensively implemented in the Yanhe River watershed, of the Loess Plateau, China, over the last six decades, and have resulted in large‐scale land use and land cover changes. This study examined the trends and shifts in streamflow regime over the period of 1953–2010 and relates them to changes in land use and soil and water conservation and to the climatic factors of precipitation and air temperature. The non‐parametric Mann–Kendall test and the Pettitt test were used to identify trends and shifts in streamflow and base flow. A method based on precipitation and potential evaporation was used to evaluate the impacts of climate variability and changes in non‐climate factors changes on annual streamflow. A significant decrease (p = 0.01) in annual streamflow was observed related to a significant change point in 1996, mostly because of significant decreases in streamflow (p = 0.01) in the July to September periods in subsequent years. The annual base flow showed no significant trend from 1953 to 2010 and no change point year, mostly because there were no significant seasonal trends, except for significant decreases (p = 0.05) in the July to September periods. There was no significant trend for precipitation over the studied time period, and no change point was detected. The air temperature showed a significant increasing trend (p < 0.01), and 1986 (p < 0.01) was the change point year. The climate variability, as measured by precipitation and temperature, and non‐climate factors including land use changes and soil and water conservation were estimated to have contributed almost equally to the reduction in annual streamflow. Soil and water conservation practices, including biological measures (e.g. revegetation, planting trees and grass) and engineering measures (such as fish‐scale pits, horizontal trenches, and sediment‐trapping dams) play an important role in reduction of the conversion of rainfall to run‐off. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamics in land cover and its effect on stream flow in the Chemoga watershed,Blue Nile basin,Ethiopia

The objective of this study was to analyse changes in stream flow patterns with reference to dynamics in land cover/use in a typical watershed, the Chemoga, in northwestern highland Ethiopia. The results show that, between 1960 and 1999, total annual stream flow decreased at a rate of 1 · 7 mm year⁻¹, whereas the annual rainfall decreased only at a rate of 0 · 29 mm year⁻¹. The decrease in the stream flow was more pronounced during the dry season (October to May), for which a statistically significant decline (0 · 6 mm year⁻¹) was observed while the corresponding rainfall showed no discernible trend. The wet season (June to September) rainfall and stream flow did not show any trends. Extreme low flows analysed at monthly and daily time steps reconfirmed that low flows declined with time, the changes being highly significant statistically. Between 1960 and 1999, the monthly rainfall and stream flow amounts of February (month of lowest long‐term mean flow) declined by 55% and 94% respectively. Similarly, minimum daily flows recorded during the three driest months (December to February) showed statistically highly significant declines over the same period. It declined from 0 · 6 m³ s⁻¹ to 0 · 2 m³ s⁻¹ in December, from 0 · 4 m³ s⁻¹ to 0 · 1 m³ s⁻¹ in January and from 0 · 4 m³ s⁻¹ to 0 · 02 m³ s⁻¹ in February (1 · 0 m³ s⁻¹ = 0 · 24 mm day⁻¹ in the Chemoga watershed). In contrast, extreme high flows analysed at monthly (for August) and daily (July to September) time steps did not reveal discernible trends. The observed adverse changes in the stream flow have partly resulted from changes in land cover/use and/or degradation of the watershed that involved destruction of natural vegetative covers, expansion of croplands, overgrazing and increased area under eucalypt plantations. The other contributory factor has been the increased dry‐season water abstraction to be expected from the increased human and livestock populations in the area. Given the significance of the stream flow as the only source of water to the local people, a set of measures aimed at reducing magnitudes of surface runoff generation and increasing groundwater recharge are required to sustain the water resource and maintain a balanced dry‐season flow in the watershed. Generally, an integrated watershed management approach, whereby the whole of the watershed can be holistically viewed and managed, would be desirable. Copyright © 2004 John Wiley & Sons, Ltd.     

Climate change and other trends in streamflow observations in Australian forested catchments since 1970

The effect of climate change on water resources has been an area of continued research, especially in Australia. Previous studies have suggested significant trends in rainfall, and these are amplified causing larger changes in streamflow. However, most of the previous analysis was based on annual time scales or modelled data and did not account for changes in land cover, which could interact with changes in climate. Climate data and streamflow data between 1970 and 2010 from 13 mostly forested small catchments (<250 km²) in Australia were analysed for trends. Non-parametric Mann-Kendall trend analysis, generalized additive mixed modelling and rainfall-runoff modelling were combined for the analysis. This indicates consistent increases in maximum temperature and varied decreases in rainfall. The streamflow in the studied catchments indicated small decreases in streamflow, which amplified observed trends in the rainfall. In general, overall decreases are much smaller than suggested in earlier research.     

Forms and drivers of annual streamflow variability in the headwaters of Canadian Prairies during the 20th century

Headwater streamflows in the Rocky Mountain foothills are the key to water availability in the Canadian Prairies. Headwater characteristics, however, have been and continue to be subject to major variability and change. Here, we identify various forms of change in the annual mean streamflow and timing of the annual peak and attempt to distinguish between the effects of multiple drivers using a generalized regression scheme. Our investigation shows that the Pacific Decadal Oscillation (PDO) is the main driver of significant monotonic trends and shifts in the central tendency of annual mean streamflow in major headwaters. In parallel, the cumulative effects of non‐PDO climatic drivers and human‐induced land use and land management are the main causes of significant variations in the timing of the annual peak. Additional analyses show that time sequences with significant trends in annual mean streamflow and timing of the annual peak coincide with those that show significant trends in the PDO or non‐PDO component of the air temperature, respectively. The natural streamflow characteristics are substantially perturbed by anthropogenic river flow regulation, depending on the form of change and/or the level of regulation. Evidence suggests that the general tendency of human regulation is to alleviate the severity of above‐ and below‐average streamflow conditions; however, it may also intensify the variability in natural streamflow characteristics during drier years and/or those with earlier annual peak timing. These are circumstances to which the regional water resource system is vulnerable. Our findings are important for the provision of effective regional water resource management in the Canadian Prairies and contribute to a better understanding of the complex interactions between natural and anthropogenic drivers in coupled human–water systems.     

Assessing the impact of climate variability and human activities on streamflow from the Wuding River basin in China

Located in the Loess Plateau of China, the Wuding River basin (30 261 km²) contributes significantly to the total sediment yield in the Yellow River. To reduce sediment yield from the catchment, large-scale soil conservation measures have been implemented in the last four decades. These included building terraces and sediment-trapping dams and changing land cover by planting trees and improving pastures. It is important to assess the impact of these measures on the hydrology of the catchment and to provide a scientific basis for future soil conservation planning. The non-parametric Mann–Kendall–Sneyers rank test was employed to detect trends and changes in annual streamflow for the period of 1961 to 1997. Two methods were used to assess the impact of climate variability on mean annual streamflow. The first is based on a framework describing the sensitivity of annual streamflow to precipitation and potential evaporation, and the second relies on relationships between annual streamflow and precipitation. The two methods produced consistent results. A significant downward trend was found for annual streamflow, and an abrupt change occurred in 1972. The reduction in annual streamflow between 1972 and 1997 was 42% compared with the baseline period (1961–1971). Flood-season streamflow showed an even greater reduction of 49%. The streamflow regime of the catchment showed a relative reduction of 31% for most percentile flows, except for low flows, which showed a 57% reduction. The soil conservation measures reduced streamflow variability, leading to more uniform streamflow. It was estimated that the soil conservation measures account for 87% of the total reduction in mean annual streamflow in the period of 1972 to 1997, and the reduction due to changes in precipitation and potential evaporation was 13%. Copyright © 2007 John Wiley & Sons, Ltd.     

Response of hydrological processes to land‐cover and climate changes in Kejie watershed,south‐west China

Land‐cover/climate changes and their impacts on hydrological processes are of widespread concern and a great challenge to researchers and policy makers. Kejie Watershed in the Salween River Basin in Yunnan, south‐west China, has been reforested extensively during the past two decades. In terms of climate change, there has been a marked increase in temperature. The impact of these changes on hydrological processes required investigation: hence, this paper assesses aspects of changes in land cover and climate. The response of hydrological processes to land‐cover/climate changes was examined using the Soil and Water Assessment Tool (SWAT) and impacts of single factor, land‐use/climate change on hydrological processes were differentiated. Land‐cover maps revealed extensive reforestation at the expense of grassland, cropland, and barren land. A significant monotonic trend and noticeable changes had occurred in annual temperature over the long term. Long‐term changes in annual rainfall and streamflow were weak; and changes in monthly rainfall (May, June, July, and September) were apparent. Hydrological simulations showed that the impact of climate change on surface water, baseflow, and streamflow was offset by the impact of land‐cover change. Seasonal variation in streamflow was influenced by seasonal variation in rainfall. The earlier onset of monsoon and the variability of rainfall resulted in extreme monthly streamflow. Land‐cover change played a dominant role in mean annual values; seasonal variation in surface water and streamflow was influenced mainly by seasonal variation in rainfall; and land‐cover change played a regulating role in this. Surface water is more sensitive to land‐cover change and climate change: an increase in surface water in September and May due to increased rainfall was offset by a decrease in surface water due to land‐cover change. A decrease in baseflow caused by changes in rainfall and temperature was offset by an increase in baseflow due to land‐cover change. Copyright © 2009 John Wiley & Sons, Ltd.     

Influences of climate,terrain and land cover on stream salinity in southeastern Australia,and implications for management through reforestation

Reforestation of cleared land has the potential to reduce groundwater recharge, salt mobilization and streamflow. Stream salinity change is the net result of changes in stream salt load and streamflow. The net effect of these changes varies spatially as a function of climate, terrain and land cover. Successful natural resource management requires methods to map the spatial variability of reforestation impacts. We investigated salinity data from 2000 bores and streamflow and salinity measurements from 27 catchments in the Goulburn–Broken region in southeast Australia to assess the main factors determining stream salinity and opportunities for management through reforestation. For groundwater systems of similar geology, relationships were found between average annual rainfall and groundwater salinity and between groundwater salinity and low‐flow salinity. Despite its simplicity, we found that the steady‐state component of a simple conceptual coupled water–salt mass balance model (BC2C) adequately explained the spatial variation in streamflow and salinity. The model results suggest the efficiency of afforestation to reduce stream salinity could be increased by more than an order of magnitude through spatial planning. However, appreciable reductions in stream salinity in large rivers through land cover change alone would still require reforestation on an unprecedented scale. Copyright © 2008 John Wiley & Sons, Ltd.     

Assessing regional land‐use/cover influences on New Jersey Pinelands streamflow through hydrograph analysis

Relative baseflow volume and streamflow flashiness indices were used to assess relationships between land use/cover and streamflow regime in nine New Jersey (NJ) Pinelands streams. Baseflow index (BFI) and Richards–Baker flashiness index (RBI) were estimated on an October–September water year, with period‐of‐record changes assessed by trend analysis and differences between watersheds assessed by examining index versus land‐use/cover relationships using a data period common to all study sites. Four streams, among the more urbanized watersheds of the nine study sites, were found to have significant (α = 0·05) trends in both indices. The two most urbanized study sites showed decreasing baseflow and increasing flashiness; however, the other two streams showed the opposite trends. An apparent slowdown in urbanization towards the second half of the streamflow period of record, along with potential changes in wetland agricultural practices in the latter two watersheds, may explain their trend results. A marginally significant (α = 0·10) decreasing relationship was found between mean annual BFI and wetland agriculture, whereas a significant (α = 0·05) increasing relationship was determined between mean annual RBI and artificial lakes/reservoirs. Principal component analysis showed an association between wetland agriculture and artificial lakes/reservoirs which suggested that both of the significant index versus land‐use/cover relationships reflect wetland agricultural activities. Because these significant relationships involved land uses/covers with small spatial extents (?5%), they demonstrated that land‐use practices can have a greater impact than spatial extent on stream hydrology. This study is the first step in assessing the effect on the NJ Pinelands stream ecology by streamflow alteration due to wetland agricultural activities. Copyright © 2006 John Wiley & Sons, Ltd.     

Long‐term sediment yield from a small catchment in southern Brazil affected by land use and soil management changes

Sediments produced from eroding cultivated land can cause on‐site and off‐site effects that cause considerable economic and social impacts. Despite the importance of soil conservation practices (SCP) for the control of soil erosion and improvements in soil hydrological functions, limited information is available regarding the effects of SCP on sediment yield (SY) at the catchment scale. This study aimed to investigate the long‐term relationships between SY and land use, soil management, and rainfall in a small catchment. To determine the effects of anthropogenic and climatic factors on SY, rainfall, streamflow, and suspended sediment concentration were monitored at 10‐min intervals for 14 years (2002–2016), and the land use and soil management changes were surveyed annually. Using a statistical procedure to separate the SY effects of climate, land use, and soil management, we observed pronounced temporal effects of land use and soil management changes on SY. During the first 2 years (2002–2004), the land was predominantly cultivated with tobacco under a traditional tillage system (no cover crops and ploughed soil) using animal traction. In that period, the SY reached approximately 400 t·km^?2·year^?1. From 2005 to 2009, a soil conservation programme introduced conservation tillage and winter cover crops in the catchment area, which lowered the SY to 50 t·km^?2·year^?1. In the final period (2010–2016), the SCP were partially abandoned by farmers, and reforested areas increased, resulting in an SY of 150 t·km^?2·year^?1. This study also discusses the factors associated with the failure to continue using SCP, including structural support and farmer attitudes.     

Impact of climate variability,drainage and land-cover changes on hemiboreal streamflow

The aim of the study was to determine the effects of climate variability, agricultural land drainage and afforestation of agricultural land on river discharge. The study was conducted in the Vienziemīte stream basin (6 km²), where discharge was monitored on a daily basis during the time period of 1946–2010. In the stream basin, natural afforestation of agricultural land began in the 1950s, and in the mid-1970s artificial drainage systems were installed in all agricultural land (70% of the total basin area). Climate variability and artificial drainage were the main factors observed to be affecting stream discharge. The changes were most evident in annual and seasonal mean, minimum and maximum streamflow. There was no effect of afforestation of agriculture land on stream discharge.     

Sensitivity of streamflow from a Himalayan catchment to plausible changes in land cover and climate

Global climate change will likely increase temperature and variation in precipitation in the Himalayas, modifying both supply of and demand for water. This study assesses combined impacts of land‐cover and climate changes on hydrological processes and a rainfall‐to‐streamflow buffer indicator of watershed function using the Soil Water Assessment Tool (SWAT) in Kejie watershed in the eastern Himalayas. The Hadley Centre Coupled Model Version 3 (HadCM3) was used for two Intergovernmental Panel on Climate Change (IPCC) emission scenarios (A2 and B2), for 2010–2099. Four land‐cover change scenarios increase forest, grassland, crops, or urban land use, respectively, reducing degraded land. The SWAT model predicted that downstream water resources will decrease in the short term but increase in the long term. Afforestation and expansion in cropland will probably increase actual evapotranspiration (ET) and reduce annual streamflow but will also, through increased infiltration, reduce the overland flow component of streamflow and increase groundwater release. An expansion in grassland will decrease actual ET, increase annual streamflow and groundwater release, while decreasing overland flow. Urbanization will result in increases in streamflow and overland flow and reductions in groundwater release and actual ET. Land‐cover change dominated over effects on streamflow of climate change in the short and middle terms. The predicted changes in buffer indicator for land‐use plus climate‐change scenarios reach up to 50% of the current (and future) range of inter‐annual variability. Copyright © 2010 John Wiley & Sons, Ltd.     

Soil erosion at three experimental sites in the ­Mediterranean

The results of erosion studies carried out at three representative sites in the European Mediterranean basin are discussed. The objectives of the study are to clarify the underlying processes affecting soil erosion and to quantify erosion and runoff in the framework of mitigation of land degradation. The study was carried out at three instrumented field stations using similar layouts and experimental set-ups and harmonized field procedures. Runoff and sediment yield from bounded plots were measured for different types of land use for longer periods. The runoff and sediment values were found to be relatively low, and showed average annual values between 2·0 and 8·9 1 m⁻² for runoff, and between 20·2 and 28·1 g m⁻² for sediment yield. The results show that the individual plot response on an event basis shows no relationship between runoff and sediment yield for two of the three sites. On an annual average basis a significant relationship is found between the runoff and sediment yield. Significant differences were observed between different types of land use, especially between semi-natural vegetation, burned and abandoned field cover types on the one hand, and agricultural fields on the other hand. The runoff and erosion values were lowest for the semi-natural fields. It was found that in non-cultivated fields the bounded plots might suffer from depletion of available sediment. It can be concluded that erosion figures are very low for the sites studied, and that the maintenance of semi-natural vegetation may help in the prevention of runoff generation and erosion. It can be concluded that the use of bounded plots may not be as ideal as might be expected from its wide application. In some cases open plots, especially under semi-natural land use, may produce much better results, especially when measuring over longer periods. Copyright © 1999 John Wiley & Sons, Ltd.     

Changes in streamflow regimes and their responses to different soil and water conservation measures in the Loess Plateau watersheds,China

Investigating the changes in streamflow regimes in response to various influencing factors contributes to our understanding of the mechanisms of hydrological processes in different watersheds and to water resource management strategies. This study examined streamflow regime changes by applying the indicators of hydrologic alteration method and eco-flow metrics to daily runoff data (1965–2016) from the Sandu, Hulu and Dali Rivers on the Chinese Loess Plateau, and then determined their responses to terracing, afforestation and damming. The Budyko water balance equation and the double mass curve method were used to separate the impacts of climate change and human activities on the mean discharge changes. The results showed that the terraced and dammed watersheds exhibited significant decreases in annual runoff. All hydrologic metrics indicated that the highest degree of hydrologic alteration was in the Sandu River watershed (terraced), where the monthly and extreme flows reduced significantly. In contrast, the annual eco-deficit increased significantly, indicating the highest reduction in streamflow among the three watersheds. The regulation of dams and reservoirs in the Dali River watershed has altered the flow regime, and obvious decreases in the maximum flow and slight increases in the minimum flow and baseflow indices were observed. In the Hulu River watershed (afforested), the monthly flow and extreme flows decreased slightly and were categorized as low-degree alteration, indicating that the long-term delayed effects of afforestation on hydrological processes. The magnitude of the eco-flow metrics varied with the alteration of annual precipitation. Climate change contributed 67.47% to the runoff reduction in the Hulu River watershed, while human activities played predominant roles in reducing runoff in the Sandu and Dali River watersheds. The findings revealed distinct patterns and causes of streamflow regime alteration due to different conservation measures, emphasizing the need to optimize the spatial allocation of measures to control soil erosion and utilize water resources on the Loess Plateau.